Power supplies typically draw current from a source of power, (such as a generator or electric utility grid, etc.). A power supply typically generates radiation that correlates with the amount of energy required by the load connected to the output of the power supply. By monitoring the current driven by the power supply, or the energy radiated from the power supply, it may be possible to ascertain the nature of the load. In some applications, however, it is desirable that the characteristics of the load be kept secret. For example, the load could be a telephone, teleprinter, or computer handling secret or classified information. Absent some precaution to secure the power supply, it may be possible for one to monitor the current provided by the power supply or the radiation emarating from the power supply and ascertain the nature of the secured load. A device for operating a power supply so that the electrical characteristics of a load cannot be determined by monitoring the energy radiated from the power supply is desirable in these circumstances.
Prior attempts have been made to develop circuits to secure a power supply. These circuits typically involve operating a complimentary load in parallel with the load that has to be kept secure. This type of circuit is illustrated in FIG. 2. The complimentary load is in parallel with the load desired to be kept secure. In this conventional arrangement, the power supply output is held at a substantially constant arbitrary level, which is at least as high as the maximum voltage required to power the true load being secured. The complimentary load is controlled in a way that ensures that the sum of the current across both loads is constant. Therefore, a constant current is driven from the power supply. Hence, if the energy radiated from the power supply is monitored, constant output will be detected, preventing the characteristics of the load from being ascertained.
The conventional circuit operates, not by isolating the power supply from the load, but rather by having the power supply operate at a substantially constant load above what is necessary for operation of the true load. Since the power supply is operating at full load capacity all the time, a large part of the energy of the power supply is wasted on a complimentary load. A second disadvantage is that this type of circuit is that it is hard to operate at high frequencies. A third major disadvantage of this type of circuit is that, in case there is more than one secure load connected to the power supply, each load requires its own complimentary load. This circuitry is not only costly but inefficient as well. Moreover, this type of circuit is relatively complex and results in a slight delay in the time the current necessary to power the true load reaches the load.
Thus, a need exists for a simple, efficient, economical, effective, and reliable secure power supply. The present invention overcomes the disadvantages of the prior art by using a "constant current" or "constant power" power supply that provides energy to an energy storage device. The load current is driven from this energy storage device but does not have any direct influence on the "constant current" or "constant power" provided to the power supply. In this system, the momentary value of the load current does not influence the current supplied by the power supply. Thus, the electrical characteristics of the load are isolated from the radiated energy spectrum of the power supply. The characteristics of the load cannot be detected by monitoring the current of the power supply.